Experiment Station Record, Volume 92, January-June, 1945 Page: 63
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1945] DISEASES OF PLANTS 63
DistribuiSao te6rica de les6es em folhas ou frutas, causadas por insetos e
outros animais ou por agentes infecciosos transmitidos por vetores (Theoretical
distribution of lesions on leaves and fruits caused by insects and other animals
or by agents transmitted by animal vectors), A. A. BITANCOURT (Arq. Inst. Biol.
[Sio Paulo], 14 (1943), pp. 243-252; Eng. abs., pp. 251-252):-When lesions on
leaves and fruits are produced by infectious agents randomly distributed on the
surface of the organs, a Poisson distribution of the number of leaves or fruits with
0, 1, 2, 3, ... k lesions is observed, provided the number of agents is not large. If,
however, lesions are produced or transmitted by an insect, for instance, a single
individual may produce more than one lesion and the distribution, if the insects are
randomly distributed, is given by expansion of the polynome P. (a + b + c + d +
. . . , where p. is the probability of there being n vectors on any leaf, as given by
the Poisson distribution, and a, b, c, d,.. . the probabilities of any insect producing
1, 2, 3, 4, ... lesions per leaf. An example is given of sweet orange leaves having
lesions of leprosis, with detailed discussion. It is pointed out that a statistical study
of the distribution of discrete lesions on leaves or fruits in virus diseases may lead
to the discovery of whether the disease in question is systemic or is locally transmitted
by a vector. In the first case the distribution may often be expected to follow
the Poisson distribution; in the second, it is thought more likely to be the one discussed
in this paper.
Diseases and pests of cereals, fibre, forage, and root crops, W. R. FOSTER
(Brit. Columbia Dept. Agr., Field Crops Cir. 17 (1942), pp. 52, illus. 13).--An
informatory manual, including control measures.
Studies on the life history of the club root organism, Plasmodiophora brassicae,
G. W. AYERS (Canad. Jour. Res., 22 (1944), No. 4, Sect. C, pp. 143-149,
illus. 27).-Attention was focused principally on zoosporangium development and
formation and discharge of zoospores. Resting spores, released from thoroughly
clubbed tissues by the action of bacteria and fungi, germinated well in tap water
at room temperature in 1-10 days; the process was hastened by exposure to frost.
Zoospores from the resting spores were biflagellate and heterokont and varied in
size. On contact with root hairs or epidermal cells of cruciferous seedlings they
settled as amebas and penetrated the cell wall to form, young thalli within the host
cells. The thallus may or may not become considerably enlarged before the protoplasm
undergoes cleavage and an irregular cluster of enlarged zoosporangia is
formed. Each zoosporangium contained 4-8 zoospores which, at maturity, were
discharged. from the root hair in the presence of free moisture; otherwise the
fungus protoplasm disintegrated. At ordinary field temperatures, 4-6 days were
required from host infection to zoospore discharge. Discharge occurred through
small openings at the point of contact of the zoosporangia with the cell wall of the
root hair. These zoospores when discharged were not over half the average
diameter of the zoospores from germinating resting spores. Temperatures most
favorable for growth of the host proved also most favorable for infection. The
cardinal temperatures for infection were 54-570, 70, and above 92 F.; only
2-2.5 days were needed for the process.
Acquired immunity from curly top in tobacco and tomato, J. M. WALLACE.
(U. S. D, A.). (Jour. Agr. Res. [U. S.], 69 (1944), No. 5, pp. 187-214, illus. 9).Cultivated
varieties of tomato became severely diseased and eventually died when
infected with this virus either via leafhoppers or grafting with other tomato plants
infected by leafhopper vectors. If, on the other hand, they were grafted with
Turkish tobacco plants that had recovered from severe stages of curly top, the
tomato plants frequently acquired an immunity similar to that in recovered tobacco.
Since the tomato plants rarely initiated the recovery reaction, this transfer of immu
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U.S. Department of Agriculture. Agricultural Research Administration. Office of Experiment Stations. Experiment Station Record, Volume 92, January-June, 1945, book, 1947; Washington D.C.. (digital.library.unt.edu/ark:/67531/metadc5064/m1/76/: accessed December 17, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.